A premixing engine supplying reformed gas fuel, obtained by premixing intake air and exhaust air in liquid fuel has conventionally been known. The premixing engine features reformation of liquid fuel into gas fuel that can be combusted in a diluted state to be combusted, and thus can achieve smaller amounts of smoke and NOx discharged, as described in Patent Literature 1 for example.
An engine described in Patent Literature 1 reforms fuel by using one of a plurality of cylinders as a reforming cylinder serving as a fuel reforming device to mix the liquid fuel with intake air and exhaust air and compressing the mixture. The reformed fuel can be reformed only when predetermined intake gas temperature, composition, compression rate, and fuel air equivalence ratio are achieved. Thus, the engine is incapable of decreasing the produced amount of reformed fuel by changing the fuel air equivalence ratio achieved by the reformed fuel or changing the intake gas amount, in accordance with an output from outputting cylinders. Thus, the engine might fail to supply an amount of reformed fuel in accordance with the output from the outputting cylinders, and thus might not be able to operate with an appropriate amount of fuel.